Fluid coke calcination utilizing an evolved hydrogen



Jan. 7, 1958 H. z. MARTIN 2,819,204

FLUID COKE CALCINATION UTILIZING AN EVQLVED HYDROGEN FilGd April 4, 1955 I6 I5 H5 PEBBLE DISENGAGING 2 mun cALc/uEn 00x5 PLUS cAsE's r0 souns RECOVERY GALE/NED #8 com 000LER 2a SULFUR-FREE 20 PM ill a0 sr l mc 04s PEBBLE FURNACE 2! 504m 46 22 run Hm 00x5 PLUS nronocsu v EXCHANGE.

ZONE I 00x5 neon t BURNER STRIPPIIIC AND FLUIDIZATION cAs I3 urr cAs I4 HOMER Z. MARTIN INVENTOR BY f M ATTORNEY FLUID COKE CALCINATION UTILIZING AN EVOLVED HYDROGEN Homer Z. Martin, Cranford, N. J., assignor to Esso Research and Engineering Company, a corporation of Delaware Application April 4, 1955, Serial No. 498,968

3 Claims. (Cl. 20231) This invention relates to improvements in calcining fluid coke. In a more specific embodiment it provides an improved process using a modified feed-to-product pebble heat exchanger system wherein hydrogen evolved in the process is utilized in the desulfurization of the coke.

There has recently been developed an improved process known as the fluid coking process for the production of fluid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions. The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. Transfer line or fluid bed reactors and burners can be used. Staged systems can be employed. In a typical operation the heavy oil to be processed is injected into the reaction vessel containing a dense, turbulent, fluidized bed of hot inert solid particles, preferably coke particles. Staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in isothermal conditions and eflects very rapid distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Product vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate. A stream of coke is thus transferred from the reactor to the burner vessel employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Suflicient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature suflicient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, is burned for this purpose. This may amount to approximately 15% to 30% of the coke made in the process. The net coke production, which represents the coke make less the coke burned, is withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch, asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically, such feeds can have an initial boiling point of about 700 F. or higher, an A. P. I. gravity of about to 20, and a Conradson carbon residue content of about to 40 wt. percent. (As to Conradson carbon residue, see A. S. T. M. testD-1894l.)

The method of fluid solids circulation described above is well known in the prior art. Solids handling technique is described broadly in Packie patent 2,589,124, issued March 11, 1952.

I United States Patent 0 The fluid coke product particles have a particle diameter predominantly, i. e., about 60 to 90 wt. percent, in the range of 20 to mesh, a sulfur content in many cases above 6 wt. percent, and a volatile content of 2 to 10 wt. percent. They have a real density of about 1.4 to 1.7 which is too low for use in the manufacture of carbon electrodes for making aluminum and other purposes. Increased density and lower sulfur and volatile contents are particularly necessary before the fluid coke is suitable for manufacture into these electrodes, one of the major uses of petroleum coke. These objectives can be obtained by calcination at elevated temperatures, e. g., 2400 F. or higher. This high temperature treatment is diflicult and expensive. It is consequently advantageous to increase the recovery of valuable products therefrom and to improve the elficiency of the process.

This invention provides an improved process for calcining fluid coke. The process comprises heating the fluid coke to a minimum temperature of about 2200 F. by countercurrently contacting the coke with gravitating hot pebbles. The coke volatiles are cracked at that temperature to evolve the hydrogen and the coke is soaked in the presence of the evolved hydrogen to desulfurize it at a minimum temperature also of about 2200 F. The desulfurized coke is cooled by contact with cooled pebbles from the coke heating step and the thus heated pebbles are further reheated for additional use.

The heating in the heat exchange zone is conducted at a minimum temperature of about 2200 F., preferably 2400 F. to 2700 F. The volatile products comprising principally hydrogen and methane are evolved and the latter is cracked to hydrogen. These volatiles are then used to treat the coke in a soaking zone at a minimum temperature of about 2200 F., preferably 2400 F. to 2700 F. for a period of time in the range of about 10 minutes to 10 hours. The sulfur content of the coke is in this manner reduced to less than about 2 wt. percent.

This invention will be better understood by reference to the example and flow diagram shown in the drawing.

The hot feed coke, e. g., coke from the fluid coke burner at a temperature of 1125 F. is sent through line 1 to the bottom portion of heat exchange zone 2. The temperature of the coke is raised to about 2700 F., for example, by the column of hot pebbles which gravitate downwardly from throat 3 at a temperature of e. g. 2830 F. and countercurrently contacts the upflowing coke particles which are e. g. in the form of a dispersed suspension. The superficial velocity of the coke particles is in the range of 0.1 to 1.0 ft./sec., e. g., 0.2 ft./sec. The evolved volatiles from the fluid coke supply a substantial portion of the required entraining gas. Small amounts of stripping gas supply the additional entraining gas requirements through line 4. The gas at 4 is for the purpose of preventing coke flow downwards into lift line 13, by which it would bypass the treating process. Stripping gases that can be used include hydrogen, methane, steam and other gases consistent with the pur pose of the end volatiles. Substantially all of the volatile matter are removed from the coke and the hydrocarbons, principally methane, cracked to coke and hydrogen.

The thus cooled pebbles Withdrawn from heat exchange zone 2 through line 12 at a temperature of 1175 F. are transported by an inert lift gas from line 14 through line 13 to pebble disengaging drum 15. The lift gases are vented through line 16. Pebbles gravitate downward from drum 15 through throat 17 to calcined coke cooler 18. The coke enters coke cooler 18 at a temperature of e. g. 2700 P. where it countercurrently contacts the cooler pebbles. The coke, unused hydrogen and vaporous sulfur-containing materials, including CS cooled to a temperature of 1225 F. are taken off through line 19 by means of entraining gas from line 30 and sent to product recovery, not shown, where the thus cooled and calcined coke is separated from the other products such as carbon disulfide and can be further cooled. The latter in turn can be separated from the other vaporous materials by means known in the art. The pebbles which have thus been heated to e. g. 2150 F. gravitate through throat 20 into pebble furnace 21.

The temperature of the pebbles is raised to e. g. 2830 F. by the combustion of any available combustible components, e. g. natural gas, torch oil, etc, from line 22 and flue gases are withdrawn through line 29. Air supports the combustion through line 23.

The heated coke and hydrogen at a temperature of e. g. 2700 F. from heat exchange zone 2 is entrained through line 25 to soaker 26. It is maintained at this temperature in this soaking zone in the form of an upflow moving bed for example 1 hour. The upflowing moving bed is maintained by a fluidizing gas through line 27 at a superficial velocity of about 0.2 ft./sec. The fiuidizing gas is kept at a minimum so as not to dilute the product. The evolved sulfurous vapors contribute toward the moving of the bed. The efliuent from line 28 contains entrained coke, the inert fluidizing gases, unused hydrogen and evolved sulfurous vapors including principally carbon disulfide. This efiluent is sent to coke cooler 18 from which it is processed as described above.

Solid inert heat exchange materials which can be utilized in the pebble heater system of this invention are generally termed pebbles. The term pebbles as used herein denotes any substantially solid, inert material 4 EXAMPLE 1 In one series of runs the temperature of calcination was varied from 1350 F. to 2700" F. while using a gas consisting essentially of hydrogen as the treating gas. The coke was treated for 30 minutes with hydrogen at each temperature as shown in Table I.

Table I.Hydr0gen calcination of fluid coke effect of temperature, 30-minute treatment Coke Sulfur, Real Temp., F. Yield, Wt. Density,

Wt. percent; 0. percent 1 Original green coke contained 7.5 wt. percent sulfur and had a density of 1.50 at: 25 C.

It is apparent from the data in Table I that temperatures of 2400 F. and above are required to get a good rate of sulfur removal.

EXAMPLE 2 Table II.--Comparis0n of hydrogen with other common gases in fluid coke calcining minute treatment) Steam vol. Treating Gas H1 H: N: N: Air Air Steam C O CO; C 04 prcent),

vol. percent) Temperature. F 2, 400 2, 700 2, 400 2, 700 2, 400 2, 700 2, 400 2, 400 2, 400 2, 400 2, 400 Coke Yield, Wt. percen 89 83 92 80 f)? 80 Sulfur, Wt. percent 4. 9 1.8 7. 4 3. 7 6. 7 2. 8 5. 2 (l. 2 5. 8 o. t: n. 7

Original green coke contained 7.5 wt. percent sulfur.

Yields not available for these runs.

of flowable size and form which has sufiicient strength to withstand mechanical pressures and the temperatures encountered within the pebble heater system. These pebbles must be of such structure that they can carry large amounts of heat from one chamber to another without rapid deterioration or substantial breakage. Pebbles which may be satisfactorily used in this treating system may be substantially spherical in shape and range from about one-eighth inch to about one inch in diameter. The pebbles are preferably of a size within the range of from one-eighth inch to five-eighths inch in diameter and have a greater free fall velocity than the col;-. Materials which may be used single or in combination in the formation of such pebbles include among others alumina, silicon carbide, periclase, beryllia, mullite, magnesia and silica.

It should particularly be noted that the process of this invention provides an extremely etficient means of utilizing hydrogen at elevated temperature in the desulfurization of fluid coke. Hydrogen has been found to be far superior to other commercially available gases utilized for the same purpose under the same conditions. Thus, for example, as explained in further detail below, air, steam, carbon dioxide and nitrogen have been found to be less eifective in terms of both yield and desulfurization.

The following examples further illustrate the advantages discussed.

Hydrogen gives high coke yields for a given reduction in sulfur content. Although yield values are not shown in Table II for air and steam, these gases are known to consume coke rapidly at these temperatures. This fact is more apparent at longer contact times.

Yields are lower for air and steam because both attack the carbon. Oxygen in the air burns the coke to give CO and steam gives CO+H by the water gas reaction.

As an illustration, one run made with air at 4500 v./v./hr. at 2400 F. and for a time of 20 minutes gave a yield of 82.5% as compared with 89% for hydrogen at a time of 30 minutes.

Another air run made at 2700 F. gave a yield of only 74.0% using a 20 minute time of treating.

It is important to note the advantage for hydrogen over all the other gases shown in sulfur content of the coke product. This holds for both 2400 F. and 2700" F. The superiority for hydrogen over nitrogen is significant in view of the fact that both are relatively inert gases insofar as any reaction with the coke is concerned.

These runs were discontinued for the most part after 30 minutes because time intervals of that nature have been found to be valid and reliable in screening tests on different gaseous materials. Varying the temperature or time of treatment or both within the prescribed ranges can bring the sulfur content down to levels required.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illus' trate how the coke was prepared.

Conditions in fluid coker reactor The advantages of this invention will be apparent to those skilled in the art. Hydrogen prepared in the process is economically utilized for the desulfurization of the coke. The utilization of a pebble furnace keeps the flue gas from the combustion step separate from the sulfur rich soaker gases. Thus the flue gases can be vented to the atmosphere without pollution problems. In addition much smaller quantities of calciner gas have to be processed for recovery.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A process for devolatilizing and desulfurizing fluid coke particles and recovering valuable products therefrom which comprises the steps of heating in a heat exchange zone the coke particles to a minimum temperature of about 2200 F. by countercurrently contacting them with gravitating hot pebbles to remove substantially all the volatile products from the coke and crack them to hydrogen; separating by entrainment the hydrogen and the coke from the pebbles and sending them to a soaking zone where they are maintained at a temperature in the range of about 2400 to 2700 F. for a period of time in the range of about 10 minutes to 10 hours so as to desulfurize the coke and evolve vaporous, sulfurcontaining products; removing an eflluent of entrained coke, hydrogen, and sulfur-containing products from the soaking zone to a cooling zone; cooling the effluent in the cooling zone by countercurrently contacting it with cooler gravitating pebbles from the heat exchange zone; separating by entrainment the eflluent from the gravitating pebbles; separating the resultant product coke from the gaseous hydrogen and sulfur-containing products; raising the temperature of the pebbles from the cooling zone in a heating zone and gravitating the thus heated pebbles to the heat exchange zone.

2. The process of claim 1 in which the heating in the heat exchange zone is conducted at a temperature in the range of about 2400" to 2700 F.

3. The process of claim 2 in which the step of heating the pebbles from the cooling zone in a heating zone is conducted by combustion.

References Cited in the file of this patent UNITED STATES PATENTS 2,432,872 Ferro Dec. 16, 1947 2,595,366 Odell et al. May 6, 1952 2,717,868 Gorin et a1 Sept. 13, 1955 2,743,218 Herrmann Apr. 24, 1956 

1. A PROCESS FOR DEVOLATILIZING AND DESULFURIZING FLUID COKE PARTICLES AND RECOVERING VALUABLE PRODUCTS THEREFROM WHICH COMPRISES THE STEPS OF HEATING IN A HEAT EXCHANGE ZONE THE COKE PARTICLES TO A MINIMUM TEMPERATURE OF ABOUT 2200*F. BY COUNTERCURRENTLY CONTACTING THEM WITH GRAVITATING HOT PEBBLES TO REMOVE SUBSTANTIALLY ALL THE VOLATILE PRODUCTS FROM THE COKE AND CRACK THEM TO HYDROGEN; SEPARATING BY ENTRAINMENT THE HYDROGEN AND THE COKE FROM THE PEBBLES AND SENDING THEM TO A SOAKING ZONE WHERE THEY ARE MAINTAINED AT A TEMPERATURE IN THE RANGE OF ABOUT 2400* TO 2700*F. FOR A PERIOD OF TIME IN THE RANGE OF ABOUT 10 MINUTES TO 10 HOURS SO AS TO DESULFURIZE THE COKE AND EVOLVE VAPOROUS, SULFURCONTAINING PRODUCTS; REMOVING AN EFFLUENT OF ENTRAINED COKE, HYDROGEN, AND SULFUR-CONTAINING PRODUCTS FROM THE SOAKING ZONE TO A COOLING ZONE; COOLING THE EFFLUENT IN THE COOLING ZONE BY COUNTERCURRENTLY CONTACTING IT WITH COOLER GRAVITATING PEBBLES FROM THE HEAT EXCHANGE ZONE; SEPARATING BY ENTRAINMENT THE EFFLUENT FROM THE GRAVITATING PEBBLES; SEPARATING THE RESULTANT PRODUCT COKE FROM THE GASEOUS HYDROGEN AND SULFUR-CONTAINING PRODUCTS; RAISING THE TEMPERATURE OF THE PEBBLES FROM THE COOLING ZONE IN A HEATING ZONE AND GRAVITATING THE THUS HEATED PEBBLES TO THE HEAT EXCHANGE ZONE. 